Effects of Fine Particulate Matter on Childhood Asthma Exacerbation in the Philadelphia Metropolitan Region

Abstract

Background: Fine particulate matter air pollution (PM2.5) is a known risk factor for asthma exacerbation. We aimed to describe the local association between PM2.5 and asthma exacerbation in the Philadelphia region, and to evaluate whether the effect is modified by children’s characteristics or other environmental exposures.Methods: We conducted a time-stratified case-crossover study of pediatric asthma exacerbation (age ≤18 years) occurring from 2011-2014, identified through electronic health records (EHR) of the Children’s Hospital of Philadelphia (CHOP) Care Network. Modeled, census-tract level estimates of daily PM2.5 concentrations were acquired from the EPA’s Downscaler model. We applied conditional logistic regression to estimate the association within warm (Apr-Sep) and cold (Oct-Mar) months, with PM2.5 level modeled as a natural cubic spline (3 degrees of freedom), and adjusting for temperature, relative humidity, and holidays. We evaluated unlagged effects (i.e., PM2.5 levels on the same day as the exacerbation) and effects lagged up to 5 days.Results: There were 54,632 asthma exacerbation events during the study period, with the majority occurring among male (60.75%) and black, non-Hispanic (58.99%) children. We found a positive association between PM2.5 and asthma exacerbation in both warm months (odds ratio [OR] comparing 90th to 25th percentile = 1.09, 95% confidence interval [CI]: 1.01-1.18, lag05) and cold months (OR, 90th vs. 25th percentile = 1.08, 95% CI: 1.04-1.12, lag0). During cold months, risk increases started from the lowest pollutant concentrations. Results were robust to multi-pollutant modeling and adjustment for additional covariates, and we found no effect modification by children’s characteristics (e.g., age, race/ethnicity, allergic rhinitis, eczema). During warm months, the PM2.5 effect was higher on days with detected tree pollen.Conclusion: We found a positive association between PM2.5 and asthma exacerbation. Our results suggest that even small reductions in fine particulate matter air pollution may reduce clinical visits for asthma exacerbation.